Compression settings for DVD from QT movies

I am going to get a company to author my DVD for me and I was to reduce the time they spend on it, and therefore cost to me. I know they will want to compress my QT files, but I don't know what settings they will want to use. Any heads up about what compression settings for DVD they will want to use in order to fir my 3 hour length project on to a duel layer disk or 2 individual disks?